I saw this a while back on tv. Really it's kind of a cruel joke no?
I can't imagine doing "nothing" though. Yet, picture a gun in your face? I guess it depends. They guy using the fire extinguisher was a quick thinker. It's hard to tell but at minimum I'd call the police. Or if I had the opportunity or felt safe enough I might try kicking the hell out of the perp enough for the victim to get away. Then again, you NEVER know until you are in the situation.
TIS